1. Field of the Invention
The present invention relates to a rotary solenoid actuator for proportionally controlling the air flow in a pipe which is used, for example, in a secondary air flow control unit or the like of an automobile. In this actuator, the angle of a rotating shaft is determined by the balance between the rotating force of a permanent magnet and the resilient force of a return spring.
2. Description of the Prior Art
One conventional linear type solenoid actuator for proportionally controlling the flow of fluid, such as air in a pipe, comprises a core, a coil wound on the core, and a plunger coaxially located within a valve housing. In addition, an air passage is formed along the axis penetrating the core and the plunger. In such an actuator, when a control current flows through the coil, the coil generates a magnetic field that causes the plunger to move towards the core. As a result, the flow of air through the pipe is approximately proportional to the control current.
However, in the above-mentioned conventional actuator, the relationship between the control current and the traveling distance of the plunger is nonlinear due to a large hysteresis, so that the flow of air is not always a linear function of the control current. In addition, the stroke of the plunger is small and accordingly, the air passage is small so that the maximum flow of air therethrough is small. Further, the flow of air is subjected to external vibration, since the plunger moved rectilinearly.